In recent years, a variety of power storage devices, for example, nonaqueous secondary batteries such as lithium-ion secondary batteries (LIBs), lithium-ion capacitors (LICs), and air cells have been actively developed. In particular, demand for lithium-ion batteries with high output and high energy density has rapidly grown with the development of the semiconductor industry, for electronic devices, for example, portable information terminals such as cell phones, smartphones, and laptop computers, portable music players, and digital cameras; medical equipment; next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs); and the like. The lithium-ion secondary batteries are essential as rechargeable energy supply sources for today's information society.
A negative electrode for power storage devices such as lithium-ion batteries and the lithium-ion capacitors is a structure body including at least a current collector (hereinafter referred to as a negative electrode current collector) and an active material layer (hereinafter referred to as a negative electrode active material layer) provided over a surface of the negative electrode current collector. The negative electrode active material layer contains an active material (hereinafter referred to as a negative electrode active material) which can receive and release lithium ions serving as carrier ions, such as carbon or silicon.
At present, a negative electrode of a lithium-ion battery which contains a graphite-based carbon material is generally formed by mixing graphite as a negative electrode active material, acetylene black (AB) as a conductive additive, PVDF, which is a resin as a binder, to form a slurry, applying the slurry over a current collector, and drying the slurry, for example.
Such a negative electrode for a lithium-ion battery and a lithium-ion capacitor has an extremely low electrode potential and a high reducing ability. For this reason, an electrolytic solution containing an organic solvent is subjected to reductive decomposition. The range of potentials in which the electrolysis of an electrolytic solution does not occur is referred to as a potential window. A negative electrode originally needs to have an electrode potential in the potential window of an electrolytic solution. However, the negative electrode potentials of a lithium-ion battery and a lithium-ion capacitor are out of the potential windows of almost all electrolytic solutions. Actually, a decomposition product of an electrolytic solution forms a passivating film (also referred to as solid electrolyte interphase) on the surface of a negative electrode, and the passivating film inhibits further reductive decomposition. Consequently, lithium ions can be inserted into the negative electrode with the use of a low electrode potential below the potential window of an electrolytic solution (for example, see Non-Patent Document 1).